1. Field of the Invention
This invention relates to a camera having an automatic focus adjusting device for automatically adjusting the focus of an objective lens.
2. Description of the Prior Art
A wide variety of cameras with automatic focus adjusting devices for automatically focusing an objective lens on an object being photographed have been proposed. Some of them have been produced and are available as manufactured articles. What is of particular importance in such cameras is that the focus adjusting operation of the objective lens by the automatic focus adjusting device and the shutter release operation that follows, that is, the exposure operation of the film, are performed in smooth succession, in other words, sequentially, without causing an unnecessary time lag between operations. In other words, wasted time in the sequence of operations delays initiation of film exposure, and in the case of a photographic camera, may result in lost opportunities for desired snap-shots.
To obtain the desired performance sequence, it is possible to construct the camera so its release button operates at two steps or positions during a single stroke. The automatic focus adjusting device is actuated at the first step of the stroke, and then the shutter release device is actuated by the second step. Thus, an exposure is initiated. Such cameras are known and disclosed in U.S. Pat. No. 3,435,744 and U.S. Pat. No. 3,442,193.
In cameras of such construction, the mere operation of the release button suffices for a continuous succession of the focus adjusting operation of the objective lens followed by the initiation of the shutter release operation. This results in a reasonable form of autofocus camera.
On the other hand, such a simple construction results in some disadvantages. In operating a camera of this construction, the operator is required first to depress the release button to the first step of the stroke and hold it, and then to be aware of whether or not the focus adjustment of the objective lens is completed. As soon as the attainment of the in-focus condition, the operator must further depress the release button to the second step. This type of operation is very troublesome. There is another disadvantage in that, for example, when the release buttom is depressed in a continuous stroke until its second step, the shutter release may be actuated before the completion of focus adjustment of the objective lens. In such a case, good photographs cannot be taken.
Accordingly, cameras of the above-described construction require, for example, a safety device for allowing the release button to be depressed to the first step, preventing further depression to the second step until the focus adjustment of the objective lens is completed and, upon receipt of a signal representative of the completion of focus adjustment of the objective lens, rendering possible the further depression to the second step. The incorporation of such a safety device in the camera complicates the mechanism and increases its overall bulk and size. In addition thereto, a further disadvantage arises from such construction of the automatic focus adjusting device. As the objective lens is axially moved, for example, from close-up settings to infinitely distant settings, the objective lens is arrested during the movement thereof to effect automatic adjustment of the focus upon the given object. The time during which the release button is stopped during its stroke after the first step by the above-described safety device changes with the object distance. Hence, the timing of the release of the shutter varies. Therefore, the operator is subjected to curious impediments when operating the camera. This may also cause the operators to experience so-called hand shake or otherwise move the camera.
Another example of a camera believed to satisfy the above-described needs, the automatic focus adjusting device is actuated by depressing the release button to initiate a focus adjusting operation of the objective lens, and, upon termination of the focus adjusting operation, a signal is produced for the shutter release device to initiate an exposure operation. Such cameras have been disclosed in Japanese patent application Laid-Open Specification No. Sho 50-38532 of Apr. 10, 1975, corresponding to U.S. Pat. No. Re. 29,599 (U.S. Pat. No. 3,917,395) filed on June 28, 1973. Such construction is also reasonable for focusing the camera, but, in application to a practical camera, the corresponding mechanism becomes very complicated. Therefore, the camera is increased not only in bulk and size thereof but also in the complexity of construction and arrangement of its internal mechanisms. Besides this, when the automatic focus adjusting device employs the method of accomplishing the automatic adjustment of the focus of the objective lens in steps, as described above, of moving the objective lens from a predetermined position in a predetermined direction, of detecting the in-focus position for the given object, and of arresting the objective lens at this in-focus position, the timing of the initiation of the shutter release is quite unstable, and depends upon the in-focus position of the objective lens. Therefore, when actuating the camera, the operator often feels subject to strange variations and may experience so-called hand-shake or otherwise move the camera.